CA1323778C

CA1323778C - Metal cutting tool

Info

Publication number: CA1323778C
Application number: CA000594535A
Authority: CA
Inventors: Harry C. Oakes
Original assignee: Unibit Corp
Current assignee: Unibit Corp
Priority date: 1988-08-04
Filing date: 1989-03-22
Publication date: 1993-11-02
Anticipated expiration: 2010-11-02
Also published as: GB2221412B; FR2635032B1; KR900002880A; SE8900905L; AU3130589A; CH678834A5; MX174242B; DE3919363A1; NL8900712A; GB8907434D0; AU635701B2; BE1006328A5; SE8900905D0; FR2635032A1; GB2221412A; JPH0248107A; US5049010A

Abstract

ABSTRACT

A metal cutting tool is disclosed which includes a cylindrical cutting body (12) having an outer cylindrical surface (13) approximating the size of the hole desired and an inner wall (14) which tapers towards a base (15). The cutter body further includes a notch (17) for removal of cutting chips which has a socket disposed on the leading edge thereof. A
carbide cutting tip (26) is disposed in the socket with the cutting tip being substantially pyramidically shaped, having a blunt cutting edge (35) extending above the cutter body. The metal cutting tool further includes a pilot bit (36) extending axially through the center of the cutter body, with the pilot including a short fluted (37) section which extends above the top of the cutting tip and provides a pilot hole for guiding the cutting tip during hole cutting. The metal cutting tool is extremely durable and is particularly suited for use with a hand held drill, providing a minimum of resistance during cutting, reducing tip binding or breakage and thereby providing smooth holes in sheet metal at field locations.

Description

': ~323778 .

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~ lo ~ - - -A METAL CUTTING TOOL

. . TECHNICAL FIEL~ . . .. .
... . .. . . . . . .. ........ .. _ _ . _ . _ _ .. . . . . .This invention relates to metal cutting tools and more particu1arly to trepannlng tools for cutting holes in sheet metal using a hand held drill.

Tools ~or cutting holes in various materials such as sheet metal generally ~all into two types, those which oparate by cutting or removing the entire interior area o~ a circle and those which operate by cutting only the circ~m~erential area of a circle t~ereby producing an interior circular plug during the cuttlng operation. A conventional fluted drill is an example o~ the ~ormer type o~ tool. Such tools have the disadvantage o~ requiring substant~ ally mor~ cutting activity in order to producQ the desired hole. Over a certain diameter, it is m~ch more ef~icient and generally quic~er to utilize a tool which cuts a thin circum~erential circle ~or removing the metal as a : 30 plug. Such tools are ~enerally ~nown as trepanning tools.
Tools o~ this type require substantially 1QSS cutting~ ~o ,, , . ~

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achieve a desired hole and therefore provide large diameter holes quicXly and with substantially less energy cons~mption.
The use of trepanning tools which cut only the circum-~ ferential area of circles-to provide large diameter holes is widely known. Such tools-generally comprise an elongated tubular cutting head having cutting blades or tips secured thereto which engage a wor~ piece to shave or cut portions thereof to define the circum~erence of a circle upon rotation of the tool. Accordingly, as cutting of a work piece is effectéd, a center plug is produced which is received in the - center area o~ the elongated tubular c~tting head. ~arious ejector devices are commonly used with such tools to remove the plug from the tool, such as spring loaded arms. Tools o~ this type have been available ~or cutting holes having diameters ranging Srom approximately less than an inch to holes ha~ing extremely large diameters ~or example up to lO inche~ or more.
Such large diameter trepanning tools are generally associated with lathe type machines which are ~ixedly mounted for pxoduc~
ing holes in an automated ~ashion. Generally, such trepanning tools ar~ therQ~ore r~gidly aligned with the matsrial to ~ cut which ~s usually al o clamped or ~ixed to prevent movement.
While such applications are well Xnown in the art, there has been a continuin~ e~ort to produc~ tools suitable ~or use in a hand held ~ashion which will provide a relatively precise and smooth hole in thin sheet metal ~or use, ~or example, in field construction such as by an electriclan in cutting holQs in ~lectrical boxes. ~n addition, it i~ d~sirabla to cut holQs in , . ., . . .. .. ... . _ _ . .. . . ..
other types Or sheet metal such as stainles~ ~teel, whlch is .. . .. . . . . . . ..

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~32377~ -~inding more use in home and building construction.
- Various efforts have been made to produce trepanning tools which can be effective in cutting holes in sheet metal in - diameters ~rom approximately 1/2 inch up to 2 inches. ~owever, such ef~orts have been generally unsatisfactory, as -it is difficult to align hand held tools ~or producing smooth rouna . .
; holes. In addition to the loss o~ rigidity, hand held drills ~ave torque and RPM limitc considerably less than those available in a fixed machine structure. Consequently, a trepanning tool for hand held applications must produce holes with a minimum o~ resistance to preclude stalling or binding.
Most o~ the tools produced to date have su~fered from rapid wear which requires ~requent replacement of either the entire tool or o~ th~ cutting tips attached thereto. For example, in U.S. Patent No. 4,490,080 to Kezran, therQ is disclosed a hole cutting tool which includes removabls cutting tips. Kezran relies on mean~ which retain the tips in slots comprising a retaining wedge which engages the leading edge o~
the slot and engages thQ leading edge o~ th~ tip to urge it against the trailing edga of the ~lot so that the cutting tip is wedged in position with the anglQ o~ the wedg~ and the angle o~ ~he trailing edg~ o~ the slot preventing outward movement o~
thQ tip. WhilQ such a trepanning tool may he of~ectiv~ in various application~, where ~leld use is complicatQd it is di~icult to provide ~or tip replacement as such tips are small and easily lost. Should a trepanning tool with dull tips be used, it would requirQ additional torque and undergo accel-~rated wear, and produce a ragged hole due to bindin~ oS the : , . . ....... . . .

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~3423~78 tips in the sheet metal.
Generally, where multi-tip tools axe used, wear may be uneven, causing binding to occur through misalignment of one or -.-~ more tips within the hole. Such binding is ~rustrating ~or the 5 tool operator,-and difficult to control with a hand held driving device, requiring additional manual..force to overcome.
Such a problem is additionally time consuming and often produces a ragged hole. Consequently, the search continues ~or a trepanning tool which is substantially wear resistant, and capable o~ producing smooth holes without binding in fLeld application using a hand held drill and to do. so .without requiring ~requent replacement. --:.

SUMMARY OF THE INVENTION
It is an ob;ect o~ the present invention to pro~ido a trepanning tool which does not require a plurality o~ cutting tips to produce a hole in sheQt metal.
It is a ~urther ob;ect o~ thH present invention to provido a trepanning tool which is capabl~ o~ producing smooth holes in sheet metal in ~ield locations using a co2mon hand held drill.
It is another ob~ect oS the present invention to .:
. provide ~ tool which is easily manu~actured, producing a tool with sub~tantially enhanc~d li~ at low cost.
It is another ob~ect o~ the present invention to provid~ a trepanning tool which c~ts holes substantially ~aster than conventional.tool , with a minimum o~ resistancQ, thereby reducing operator ~atigue.
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- 5 13237~8 Accordingly, a metal cutting tool is disclosed which comprises a cylindrical cutter body which is substantially the _ diameter of the desired hole. The cutter body includés an - outer wall and an inner wall which tapers inwardly ~rom a cutting end to a base in the cutter-body, with the inner and outer walls joined at a forward edge thereo~. The cutter body includes a notch extending about the length thereof for removing cut material therefrom. A socket is disposed on one - wall of the notch, with the socket sized to accept a cutting tip therein. The body ~urther includes an axially disposed bore extending therethrough for inclusion o~ pilot means which align the cuttinq tool with the desired holQ location. The cutting tip is substantially pyramidically shaped and includes a blunt cutting edge which extends above the cutter body, ~urther including a bottom and rear wall ~or mating with the socket in the cutter body.

., BRIEF DESCRIPTIO~ OF ~HE DRAWI~GS
Fig. 1 is an enlarged perspectiv~ ~iew oS the ~etal cutting tool o~ th~ present invention.
Fig. 2 1~ a longitudinal cross-sectional ViQW Or the cutting tool o~ the present invention illustrating the location and placement o~ the cutting tip within the cuttar body, taken along thQ line 2-~ o~ Fig. 1.
2S Fig. 3A is an enlarged front YieW, 3B, an enlarged side view, and 3C, an enlarged top view o~ the cutting tip located in the cutter body.
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DETAILED oEscRIpTIoN OF THE INvENTIQ~
. Referring to Figs. 1 and 2, the metal cutting tool of the present invention is shown. The tool 10 includes a drive : - .- engaging section 11, and a cutter body 12. The drive en~aging S section may be of any suitable shape for engaging a conYemtion-- al drill chuck common, ~or example, to 3/8 or 1/2 inch drive . drills.
The cutter body 12 includes an outer cylindrical surface 13, essentially matching the size of the hole desired, with the cutter body further including an inner, inwardly tapered sur~ace 14 which joins at a base 15. The inner .and outer surfaces join at a forward edge 16 o~ cutting body 12.
Having an inwardly tapered surface allows plug discharge without requiring auxiliary plug removers such as sprin~ loaded lS arms. Essentially, a~ a plu~ is cut, it tends to bow du~ to the cutting pressure, which ~orces the plug into the cutting body. A~ter th~ plug is rsleased ~rom ths shest metal, it is driven by its own resiliency, acting on ths tapered sur~acQ to sel~ discharge, an important ~eature rOr ~isld operation.
Generally a taper o~ ~rom 10-40 degrees may be used with about 27 degrees preferred in a 7/8 inch diametsr tool.
The cutter bcdy further lncludes a notch 17 sxtending rrom the ~orward edge 16 to the drive section 11 o~ the cutter body. Ths notch 17 is essentially rectangular, including sides ~ 25 1~ and 19, and a bottom 20. While a rectangular notch is shown, it will ~e und~rstood that other shaped notches may also be used. .The notch i5 pra~era~ly narrow, ~or example, on ths.
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` order o~ about 0.25 inches wide in a 7/8 inch tool, to prevent . . . . . . , . . , - ~ . .- , , - ........................... ..
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hooking during hole cutting. A leading edge 21 o~ the side 18, in reference to the rotation o~ the tool, includes a socket 22 ha~ing a bottom wall 23 and a side wall 24, with the socket : sized to accept a cutting tip therein. The cutter body further incl~des a concentric ~ore 25 extending from the drive end through the base 15 o~ the cutter body.
. Generally, the cutter body may be composed o~ steel, - alloy or a high carbon steel kno~n as ~tool steel~, and is preferably composed of A.I.S.I. 6150 steel, heat treated for maximum hardness and toughness.
-The metal cutting tool includes a cutting tip 26 which is secured in the soc~et 22. Referring to Figs. 3A-3C, the cutting tip 26 includes an outer wall 27 which is straight sided to essentially match the o~ter wall 13 of the cutter body 12. The tip outer wall 27 may optimally include a beveled outer leading edge ~or assurinq that a smooth sided hole is provided during through cutting. The cutting tip further includes a bottom wall 29 and a rear wall 30 which mate with the bottom wall 23 and sida wall 24 o~ the socket 22. In a pre~erred embodiment, best seen in Fig. 3A, tha rear wall to bottom wall ~unction is curved rather than square edged in order to aasure proper alignmsnt and maximize distribution o~
the cutting forces over the sur~ace o~ the cutter body. ~he bottom wall and rear wall should also be sized to provide a maximum sur~ace area ~or bonding. For exa~ple, a bottom width o~ about 0.165 inches and a rear wall height o~ about 0.265 inches, ~oined with a radiu~ of about 0.0625 inches, provides a . . . , -..................................... . . , .... : .
~large surface area for assuring ~irm bondin~ in a 7/8 inch , . .. . . . . . . . ... .. _ .. .

8 132377~
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diameter tool.
~ he cutting tip further includes a flat ~ront face 31 which is generally in alignment with the side wall 18 of the notch 17.- The carbide tip also includes an inwardly sloped S wall.32, tapering towards.the base 15 o~ the c~tter body, which joins with a vertical section 33 forming an essentially pyramidically shaped tip. The wall 32 tapers essentially in - about the same amount as the cutter body inner wall! i.e. about 10-40 degrees, with 30 degrees pre~erred Sangle D). The carbide tip further includes a top ~lat sur~ace 34 which slopes and tapers rearwardly in the direction o~ rotation. The top surface slope may be fairly steep, on the order o~ about 5-20 degrees, sloping rearwardly until the back of the top surface 34 is essentially flush with the forward edg~ 16 o~ thQ cutter - 15 ~ody 12 (see Fig. 3A, angle A). For example, in a 7/8 inch tool, an 8 degree slope may be used. Similarly the taper may vary with tool size, being dependent on the desired clearance, with inner and outer tapers of 5-15 degree~ possible (SeQ Fig.
3B, angles B and C). Again, for a 7/8 inch tool, an inner 20 taper o~ lO degree~ (~), and an outer taper o~ 12 degrees (C?
are exemplary, with tha di~ference in taper angle resulting ~rom the di~erence ln radiu~ between the inner and outer walls.
A blunt cutting edge 3S is formed at the junction of - 25 the ~ront face 31 with the top surface 34. The tip, at the cutting edge 3S, extends above the ~orward edge of the cutter _ . body, generally from 0.010 to 0.020 inches. For ex~ple,.in a 7~8 inch tool ~or c~tt~ng sheet metal up to 0.14 lnche~ thlck, :: . . . . - . , .

9 132377~
the tip extends about 0.015 inche~ above the ~orward edge of the cutter body. The cutting edge may be ~rom 0.05 to 0.10 inches wide, wit~ the top surface narrowing in the direction o~
rotation until it approximates the width o~ the cutter body forward edge, i.e. a~out 0.04 ihches. T~e blunt cutting edge provided by this geometry is substantially more durable than the poir.ted cutting ed~es common to other tools which are prone to rapid wear or breaXage. For t~e illustrative 7/8 inch tool, the cutting edge is preferably about 0.07 inches wide.
The cutting tip may be composed of tungsten car~ide such as industry code number C-10, and is preferably composed of micro fine grain tungsten cobalt carbide. The cutting tip may be brazed, welded or otherwise bonded to the cutter body to assure that the tip does not move during cutting. Generally, brazing i5 pre~erred for bonding the tip to the cutter body, providing an economic yet reliable means of producing the metal cutting tool.
Re~erring to Fig. 2, the metal cutting tool o~ the present invention Surther includes a pilot drill bit 36 disposed within the bore 2S extending th-ough the cutter bcdy 12. Such a pilot bit includes a ~luted section 37 which pre~erably has a double sided fluta and a pointed end 38. A
135 degree spli~ point ig pre~erred to assure proper hole placement without requiring a prick punch ~ark. The pilot bit i~ a modi~ied version o~ a common ~ody drill used in the sheet metal tr~de, having no ~argin or clearance which i~ co~mon to twist drills. Generally, i~ a common twist dri?l with standard . . .
fluted end werQ used~ the side thrust generated by the trepann :

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lo 1 323778 ing tool cutting edge would cause the drill to cut on the side as an end mill, quickly producing an oversized egg shaped pilot hole which could allow the carbide tip to bind, producing a ragged hole. The pilot ~it therefor~ includes a limited flute section to allow for first cutting a pilot hole using the ~luted end and then insertion o~ an un~luted shaft section 39 within the pilot hole for guiding the cutting tip in the proper orbit without the side thrust causing hole enlargement.
The fluted section extends for at least the depth of the maximum gauge sheet metal ~or which the tool is designed, with about 0.25 inches generally adequate for most applica-tions. The fluted section extends above the maximum height of the tip to allow the fluted end to disengage from the sheet metal prior to the tip contacting the sheet metal. In a pre~erred embodiment, shown in Fig. 2, the pilot is double ended, having a second ~luted section 37a. ~he pilot may be removed by loosening a locking screw 40 which i5 engageable with a recess 41, allowing removal o~ the pilot and exchange o~
the dull end with a sharp end.
The m~etal cutting tool o~ the present invention is particularly suited ~or ~ield use using a hand held driver such as a standard drill, being surprisinqly durable and therefos~
capable o~ long term use. Utilizing a blunt cutting edg~ ~
prov$des a smooth hole with a minimum o~ resistance, while substantially increasing wear resistance. In addition, limiting the metal cutting toal to a single tooth dQsign _ prevQnt~ uneven w¢ar, ~urther reducing the potential ~or binding. Placinq such a tip with a large bonding area in the .., ..... , . . , _ , -, . . .
-- , . . .. _ _ _ .. _ . . : . . .. _.. ._. .. . . .. _ , , _ _ . . . ._ _._. .

11 13237~8 cutting body previously de-cribed assures firm holdln~ o~ the tip with a minimum o~ distortion, thereby reducing the chances for breakage. The shape of the cutter body also presents~an ~~- outside body surface whioh ~ubs in the cut such that any mis-alignment caused by the lack o~ rigidity in the hand heldoperation causes a reYerse thrust to return the tool to the proper orbit. Utilizing a narrow notch prevents the notch from hooking wh~n the hand held drill is tipped at an angle to the hole axis, allowing intersecting holes to be drilled without binding, 50 long as a pilot hole can be pro~ided. The tapered inner wall o~ the cutter body also provides near automatic discharge of the cut plug without re~uiring auxiliary devices.
While the preferred embodiment sf the present invention has been described in relation to a metal cuttinq tool includ-1~ in~ a rectangular notch and a particularly shaped cutting tipextending from a cuttsr body, it will be understood by those skilled in the art that other similarly shaped cutting tips, notches or pilot bits can be used without varying ~rom the scope o~ the present invention. ~n addition, it will be undQrstood by those s~illed in the art that the means ~or attaching to a drive member such a~ a hand held drill may vary in accordance with the various drill chuc~s ~ommon to the art.

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Claims

1. A metal cutting tool for trepanning holes in sheet metal utilizing a hand-held drill as a drive device, the cutting tool comprising.
a cylindrical cutter body including a cylindri-cal outer wall which is substantially the diameter of the desired cutting hole, the cutter body further including an inner wall which tapers inwardly from a cutting end to a base in the cutter body, with the inner and outer walls joined at a forward edge thereof, the cutter body further including a notch extending about the length thereof for removing cut material therefrom, a socket disposed on a wall of the notch at a cutting end of the cutter body, the socket size to accept a cutting tip therein, the cutter body further including an axially disposed bore extending therethrough, and further including drill-engaging means for releasably engaging with the drill;
a cutting tip disposed within the socket, the cutting tip being substantially pyramidically shaped and including a blunt cutting edge extending above the cutter body, the cutting tip further including a bottom and rear wall for mating with the socket in the cutter body; and, pilot means, disposed within the axial bore extending through ths cutter body, for aligning the cutting tool at the desired hole location.

2. The metal cutting tool of Claim 1 wherein the notch is essentially rectangular in shape.

3. The metal cutting tool of Claim 1 wherein the socket includes a bottom wall and a side wall which are sized to accept a cutting tip therein.

4. The metal cutting tool of Claim 1 wherein the cutter body is composed of steel.

5. The metal cutting tool of Claim 4 wherein the cutter body is composed of tool steel, heat-treated for hardness and toughness.

6. The metal cutting tool of Claim 1 wherein the cutting tip includes an outer wall which is essentially alignable with the outer wall of the cutter body, further including an inner wall which inwardly slopes from an upper end thereof, joining with a vertical wall which is parallel to the outer wall of the cutting tip, the cutting tip further includ-ing a front face which joins with a top cutting surface to form the blunt cutting edge.

7. The metal cutting tool of Claim 1 wherein the cutting tip extends above the top surface of the cutter body by at least 0.005 inches at the cutting edge thereof.

8. The metal cutting tool of Claim 6 wherein the cutting tip includes a top cutting surface which is essentially flat, the cutting surface tapering and sloping from front to back relative to the direction of rotation.

9. The metal cutting tool of Claim 1 wherein the blunt cutting edge is from 0.050 to 0.010 inches wide.

10. The metal cutting tool of Claim 1 wherein the cutting tip has a top cutting surface which tapers from front to rear from about 5-15 degree relative to the cutter body.

11. The metal cutting tool of Claim 11 wherein the top cutting surface slopes from front to rear at about 8 degrees.

12. The metal cutting tool of Claim 1 wherein the cutting tip is composed of tungsten carbide.

13. The metal cutting tool of Claim 1 wherein the cutting tip is composed of micro-fine grain tungsten cobalt carbide.

14. The metal cutting tool of Claim 1 wherein the pilot means comprise a pilot bit including a fluted section for drilling a pilot hole, the fluted section provided above the height of the cutting tip, the pilot bit including a cylindri-cal shaft section from which the fluted section extends, wherein a pilot hole is provided by the fluted section with the cylindrical shaft section entering the pilot hole prior to the cutting tip contacting the sheet metal.

15. The metal cutting tool of Claim 15 wherein the pilot bit includes a 135 degree split point for providing a pilot hole without requiring a prick punch.

16. The metal cutting tool of Claim 16 wherein the pilot bit includes limited fluted sections at opposite ends thereof, the bit including locking means for holding within the cutter body bore, the locking means symmetrical therewith in order to allow removal of the pilot bit and switching of the fluted ends after one end becomes dull.

17. A metal cutting tool for trepanning holes in sheet metal utilizing a hand held drill as a drive device, the cutting tool comprising:
a cutter body including a cylindrical outer wall which is substantially the diameter of the desired cutting hole, the cutter body further including an inner wall which tapers inwardly from a cutting end to a drive end of the cutter body with the inner and outer walls joined at the cutting end at a top surface, the cutter body further including a notch extend-ing about the length thereof for removing cut material, a socket, disposed on one wall of the notch at the cutting end of the cutter body, the socket sized to accept a cutting tip therein, the cutter body further including an axially disposed bore extending therethrough and further including a drill engaging means for releasably engaging with the drill;
a cutting tip disposed within the socket, and including an outer wall which is essentially alignable with the outer wall of the cutter body, an inner wall which inwardly slopes from an upper end thereof, joining with a vertical wall which is parallel to the outer wall of the cutting tip, the cutting tip further including a front face, the tip including a mating wall which corresponds to the socket in the cutter body, the cutting -tip including a top cutting surface which is essentially-flat, the cutting surface tapering and sloping from front to back relative to the direction of rotation, a blunt cutting edge provided at the junction of the top cutting surface with the front face, the cutting tip extending above the forward edge of the cutter body by at least 0.005 inches at the cutting edge thereof: and pilot means disposed within the axial bore extending through the cutter body.

18. The metal cutting tool of Claim 17 wherein the pilot means comprise a pilot bit, including a fluted end for drilling a pilot hole, the fluted end extending above the height of the tip, the pilot bit including a cylindrical shaft section which enters the pilot hole prior to the tip contacting the sheet metal, the pilot bit thereby guiding the tip for assuring that an essentially smooth round hole is formed.